#!/bin/bash
function addem() {
    if [ $# -eq 0 ] || [ $# -gt 2 ]; then
        echo -1
    elif [ $# -eq 1 ]; then
        echo $(($1 + $1))
    else
        echo $(($1 + $2))
    fi
}
echo -n "Adding 10 and 15: "
value=$(addem 10 15)
echo $value
echo -n "Let's try adding just one number: "
value=$(addem 10)
echo $valueecho -n "Now trying adding no numbers: "
value=$(addem)
echo $value
echo -n "Finally, try adding three numbers: "
value=$(addem 10 15 20)
echo $value
